1. Field of the Invention
The present invention relates to a characteristic correction system for a fuel pressure sensor in an in-cylinder injection-type internal combustion engine that directly injects fuel that has been accumulated/pressurized in a high-pressure fuel pipe into a combustion chamber, wherein the characteristic correction system for a fuel pressure sensor corrects a fuel pressure sensor characteristic used to adjust a correction of a fuel injection amount, and to adjust the fuel pressure in the high-pressure fuel pipe.
2. Description of the Related Art
In recent years, there has been used an in-cylinder injection-type internal combustion engine, in which an injection hole of a fuel injection valve is mounted facing in the combustion chamber, and fuel is directly injected into the combustion chamber by means of the fuel injection valve.
This type of internal combustion engine is composed of a low-pressure fuel pump, a high-pressure fuel pump, a low-pressure regulator, a high-pressure fuel pipe, a fuel pressure control valve and a fuel injection valve.
The low-pressure fuel pump sucks up the fuel from the fuel tank and discharges the relatively low-pressure fuel. The high-pressure fuel pump sucks up the low-pressure fuel discharged by the low-pressure fuel pump, and discharges relatively high-pressure fuel.
When the discharge pressure from the low-pressure fuel pump has risen sufficiently, the low-pressure regulator adjusts the fuel pressure to a low-pressure set value, and the high-pressure fuel pipe accumulates/pressurizes the high-pressure fuel that the high-pressure fuel pump discharges.
The fuel pressure control valve adjusts the pressure of the fuel that is accumulated/pressurized in the high-pressure fuel pipe to a given value, and the fuel injection valve injects into the combustion chamber the high-pressure fuel which has been adjusted by the fuel pressure control valve.
Further, the internal combustion engine is provided with a fuel pressure sensor for detecting the pressure of the fuel that is accumulated/pressurized in the high-pressure fuel pipe. By performing a feedback control on the fuel pressure control valve so that the correction of the injected fuel amount and the fuel pressure in the high-pressure fuel pipe respectively take a given value, the combustion state and the operating state in the internal combustion engine are optimally controlled.
Thus, in order to achieve the object of optimally controlling the combustion state and the operating state of the internal combustion engine, it is extremely important to maintain the detection precision of the fuel pressure sensor. Therefore, various techniques for compensating the detection precision have been proposed.
For example, JP 10-9073 A proposes a method in which, when the discharge pressure of the low-pressure fuel pump rises sufficiently and the high-pressure fuel pump is substantially in a non-drive state, a detected value from the fuel pressure sensor is corrected so as to correspond with the low-pressure set value that is adjusted by the low-pressure regulator.
Also, JP 10-37789 A proposes a method comprising two fuel pressure sensors each having detection ranges with different sizes, in which the detected values from the two fuel pressure sensors are compared to each other to correct the detected values from the fuel pressure sensors.
The conventional fuel pressure characteristic correction system is as described above. Namely, in the correction method proposed in JP 10-9073 A, no consideration is given for variation in the adjustment pressure and in the discharge flow rate due to manufacturing tolerance and deterioration of the low-pressure regulator and the high-pressure fuel pump, nor is consideration given for deterioration of the detection precision due to manufacturing tolerance and deterioration of the fuel pressure sensor. Therefore, there is a danger that the low-pressure set value itself, which is used as a reference pressure when correcting the fuel pressure sensor, is off mark. Thus, when the fuel pressure sensor is corrected while the low-pressure set value is off mark, the correction ultimately becomes an erroneous correction, and there was a problem in that the precision of the fuel injection amount and the controllability of the fuel pressure adjustment would deteriorate.
Further, the correction method proposed in JP 10-37789 A requires multiple fuel pressure sensors, and there was a problem in that it became too expensive. Further, compared to the fuel pressure sensor with the larger detection range, the detection member of the fuel pressure sensor with the smaller detection range always exhibits a greater amount of distortion. Therefore, there was a problem in that its durability might decrease.
The present invention has been made to solve problems such as those mentioned above, and therefore has as an object to obtain a characteristic correction system for a fuel pressure sensor, which compensates the detection characteristic of the fuel pressure sensor to a high precision level, from the beginning through aged deterioration.
The characteristic correction system for a fuel pressure sensor according to the present invention includes a high-pressure fuel pump for sucking up low-pressure fuel pumped out from a fuel tank and discharging a high-pressure fuel, a high-pressure fuel pipe for accumulating/pressurizing the high-pressure fuel, a fuel pressure control valve for adjusting a fuel pressure of the high-pressure fuel to a given value, a fuel injection valve for directly injecting into the combustion chamber a high-pressure fuel which has been adjusted by the fuel pressure control valve, pressure release valve for equalizing a pressure in the high-pressure fuel pipe at a known gas pressure. And further includes a fuel pressure sensor for detecting the pressure in the pipe, and a control unit for calculating a correction value for a detected value from the fuel pressure sensor, based on a pressure differential between the pressure in the pipe and the gas pressure, wherein the control unit opens the pressure release valve, and when the pressure in the pipe becomes equal to the gas pressure, the gas pressure is used as a reference value to calculate the correction value.
Therefore, it becomes possible to easily and precisely perform the correction in light of the deterioration in the detection precision level arising from the manufacturing tolerance and the deterioration of the fuel pressure sensor and the like.
Further, the characteristic correction system for a fuel pressure sensor according to the present invention includes a high-pressure fuel pump for sucking up low-pressure fuel pumped out from a fuel tank and discharging a high-pressure fuel, a high-pressure fuel pipe for accumulating/pressurizing the high-pressure fuel, a fuel pressure control valve for adjusting a fuel pressure of the high-pressure fuel to a given value, a fuel injection valve for directly injecting into the combustion chamber a high-pressure fuel which has been adjusted by the fuel pressure control valve. And further includes a fuel pressure sensor for detecting a pressure in the high-pressure fuel pipe, and a control unit for calculating a correction value for a detected value from the fuel pressure sensor, based on a pressure differential between the pressure in the pipe and the gas pressure, wherein the control unit calculates the correction value in a case where the detected value is equal to or less than a pressure of atmospheric pressure.
Therefore, in the range of characteristic variation exhibited in the fuel pressure sensor, when the detected value from the fuel pressure sensor indicates a negative pressure that is equal to or less than the atmospheric pressure and which is not actually possible, this detected value is immediately corrected to a characteristic that is within the range that is actually possible.